The present invention relates to a distributed processing ISDN (Integrated Services Digital Network) switch. More particularly, the present invention relates to a packet switching system for executing multimedia packet switching with a distributed processing ISDN switch by implementing shared use of packet assembly/disassembly control units within the switch with respect to individual terminal lines, assigning packet assembly/disassembly control units to each of different types of media, and installing in the switch a message bus for transferring non-packet data and a packet bus for transferring packets.
An ISDN architecture is an implementation for promoting versatile and advanced communications services. A current trend in the ISDN art is toward a distributed processing ISDN switch having various control functions which are distributed to a plurality of processors in place of a traditional functionally centralized type of ISDN switch. Elaborated to distribute the functions and loads, a distributed processing ISDN switch features various merits such as feasibility to modular applications, building block capability, and high reliability. A packet switching system is capable of processing multiple media collectively, and there is an increasing demand for such a switching system in the ISDN switches field. When packet switching is adopted for an ISDN switch, highly efficient use of the lines and, therefore, an extremely effective network can be constructed if packets are transferred over trunks.
A prior art distributed processing ISDN switch has terminal line control units, each being associated with respective one of terminal lines, for effecting B channel and D channel line control. Trunk control units are assigned one-to-one to the trunks to execute X.25 protocol line control. The terminal line control units and trunk control units are interconnected by a packet transfer bus. A call control section for performing call processing is connected to the line control units by a call control bus which is adapted to transfer call control data. Each of the terminal line control units is provided with a packet assembly/disassembly control unit. All the information in the form of data or voice, for example, which come in over any of the lines is assembled or disassembled by the exclusive terminal line control unit assigned to that line, the resulting packets being transferred over the packet bus. The prior art ISDN switch is, for example, proposed in U.S. Pat. No. 4,827,473.
A drawback with the prior art ISDN switch described above is that packet assembly/disassembly control units have to be assigned one-to-one to the terminal lines. Further, as the number of media to be handled by the switch increases, packet assembly/disassembly control units, each being capable of dealing with a particular type of media, have to be installed on a terminal line basis. Then, a voice packet assembly/disassembly control unit would exist even in, for example, a terminal line control unit which does not accommodate a terminal having a voice communications capability, resulting in a redundant functional distribution. On the other hand, when data are interchanged without being accompanied by voice, the voice packet assembly/disassembly control unit is not used at all, resulting in the functional utilization efficiency in the switch being low. Hence, a packet switching system of the type installing packet assembly/disassembly control units in individual terminal line control units of a switch to assign the whole packet assembly/disassembly processing operations to the terminal line control units has a problem left unsolved as to how to distribute the packet assembly/disassembly processing functions within the switch. That is, distributing the packet assembling/disassembly functions to the terminal line control units is not desirable.
As discussed above, the packet assembly/disassembly control units have to be installed in a switch in association with different types of media because the content of packet assembly/disassembly processing differs from one media to another. Nevertheless, what is required of the packet switching system for a distributed ISDN switch is to enhance efficient use of packet assembly/disassembly control units without installing the packet assembly/disassembly control units in the individual terminal line control units for accommodating various types of media.